Resonation

The buzz created by the vocal folds resonates (vibrates) the air column and
this in turn causes the structures above and around the larynx to vibrate/resonate
as well.

Remember from Phonation that the vocal folds
vibrate and chop the air stream into little puffs of air. The rate or frequency
at which these puffs come out is very fast - from 32 cycles per second or
Hertz (Hz) for a very low bass to 3136 Hz for a very high soprano. We speak
somewhere between 98 Hz and 262 Hz. This rate is called the fundamental
frequency.

Almost anything can vibrate, and will vibrate at a natural frequency,
that is at a rate that is most conducive to its vibrating. A good example
of natural frequency can be seen on a backyard swing: no matter how hard you
push the swing, the rate of frequency of swinging is the always same, no matter
how far you travel each time. Another familiar example is the tuning fork.
It vibrates most powerfully and the longest at its natural frequency. In the
same way, the various structures and tissues of the body, resonate more easily
at certain pitches.

You can feel this by tilting your head back and saying, in a low voice,
"Awwwww". Put a hand on your chest and feel it rumble. Now tilt
your head forward, place a hand on your head and say, "Heeeeeeeeeee"
in a high voice. Feel the vibrations in your skull?

The parts of the body that can vibrate in harmony with the voice are often
called Resonators.

The Air Column
Extending from your larynx to your lips, the air column vibrates
at a natural frequency - in much the same way that the pipes of an organ do.
As you shorten the organ pipe, and thus the air column, the pitch gets higher.

Try blowing across a bottle and then adding water and blowing again -
observe how the pitch rises.

In speech, the rate of vibration of the vocal folds creates the
fundamental frequency, or pitch of the the sound. The frequency or frequencies
at which the air column vibrates determines the quality
of the tone.

In fact, the air column from the larynx to the lips functions very much like
a uniform tube, without much variation in width. In an average adult, the
tube is approximately 17.5 cm long in adult males and 14.7 cm long in adult
females. Apparently the approx. 90° bend seems to make no difference acoustically.

The sound created by the vocal folds isn't a pure tone - it is complex. It
is made up of the fundamental frequency (the rate at which the folds vibrate)
and a number of partials, which are harmonics of the fundamental
frequency, vibrating 2 times, 3 times, 4 times, etc... as fast as the fundamental.
Our voices are made up of a spectrum of the fundamental and these "overtones".

Formants
Physics tell us that our tube, which functions as if it is closed at one end
(since the larynx closes it off at the bottom), naturally resonates at the
odd numbered multiples of the fundamental. That is, if the fundamental is
100 Hz, the partials will resonates at 300Hz, 500Hz, 700Hz, etc... These "standing-waves"
of sound are also known as formants, and are labelled F0
for the fundamental frequency, F1 for the first formant, F2
for the second formant, F3, etc. In shaping speech, the first three
formants are most important. In a way, it is as if each vowel is a "chord"
-- like playing three notes together on the piano, where the bottom note stays
the same and the notes above change.

Remember, we saw that :

"the rate of vibration of the vocal folds creates the fundamental
frequency, or pitch of the the sound. The frequency or frequencies at which
the air column vibrates determines the quality of the tone."

What we recognize as "vowels" are actually changes in the quality
of the tone. Our tongues allow us to change the shape of the "tube",
specifically changing the cross-sectional "width" by sliding forward
or back.

Try shortening it by pulling back into an [u]/"oo" (as in "mood"):
the tongue is pulled back here. (Notice how the degree of lip-rounding also
affects the sound?)

Try going back and forth from "EE" to "oo", keeping
the same pitch throughout. As you tongue slides back towards the "oo"
you may hear how part of the sound drops in pitch, even though your F0,
fundamental frequency remained the same.

You can hear you that by saying "uh" and "er", lifting
and lowering your tongue tip.

The use of harmonics can be emphasized and focussed to make a beautiful form
of singing, called Overtone Singing. There are many styles of this,
including the chanting of Tibetan Monks, Throat Singing & Khoomei and
a Western-ized style. Exploring these vocal style can really expand a performer's
range in terms of the sound qualities available.

Resonators
The following areas vibrate "sympathetically" with the air column.
The way in which each area vibrates acts as a cue to the quality of the sound
created, giving tactile motor feedback to the brain, which works in conjunction
with the hearing mechanisms.

What is perceived or described by voice teachers as "placement"
of the voice, generally describes how the vibration of the air column interacts
with these structures to accentuate or diminish the size of the second and
third formants ( F2 and F3 ). The term "placement"
indicates where one feels the augmented vibration due to the change the relationship
of the formants to areas of the body.

The following is a list of Resonators and the pitches or vocal qualities
that most easily activate them

Chest and Lower Body - low pitches and open sounds ("AW")

Throat - mid-range, easy speaking tone

Mouth - upper mid-range, mid-vowels

Nasal - close, front vowels, especially when followed by a nasal
consonant

Facial - high range, front vowels

Sinus - given that there are so many sinuses, many different quality
sounds activate them

More on Resonation:

Music
Acoustics on the Threshold of the 21st Century
Johan Sundberg, the expert on music accoustics puts it all in perspective
in this page base on a talk given in Braunschweig, in December 1996. Excellent
images and examples, if a bit technical. Also explains the singer's formant.
posted May 27, 98.